Prior art piezo-electric speakers have perfect circle piezo-electric members to generate a vibration in accordance with an electric signal applied to the member. Also, they include perfect circle piezo-electric vibration plates adhered to the piezo-electric member to convert the vibration to sound. The piezo-electric vibration plate has a uniform thickness and has a vibration center adapted to coincide with the center of the piezo-electric member (see Japanese Laid-open Patent Publication No. 22395/1994).
In prior art piezo-electric speakers, however, since the piezo-electric vibration plates can vibrate but are made of a metallic material with less stretchability, when sound pressure is increased, no vibrating or a spurious vibration may be generated in some parts of the piezo-electric vibration plate. This causes a distortion, such as a crease generated during vibration, so that it is difficult to ensure uniform broad-band sound pressure.